Brain-derived neurotrophic factor prevents low-frequency inputs from inducing long-term depression in the developing visual cortex

Brain-derived neurotrophic factor (BDNF) is reported to enhance synaptic tr ansmission and to play a role in long-term potentiation in hippocampus and neocortex. If so, a shortage or blockade of BDNF might lead to another form of synaptic plasticity, long-term depression (LTD). To test this possibili ty and to elucidate mechanisms if it is the case, EPSCs evoked by test stim ulation of layer IV were recorded from layer II/III neurons in visual corti cal slices of young rats in the whole-cell voltage-clamp mode. LTD was indu ced by low-frequency stimulation (LFS) at 1 Hz for 10-15 min if each pulse of the LFS was paired with depolarization of neurons to -30 mV but was not induced if their membrane potentials were kept at -70 mV. Such an LTD was b locked by exogenously applied BDNF, probably through presynaptic mechanisms . Suppression of endogenous BDNF activity by the anti-BDNF antibody or an i nhibitor for BDNF receptors made otherwise ineffective stimuli (LFS without postsynaptic depolarization) effective for LTD induction, suggesting that endogenous BDNF may prevent low-frequency inputs from inducing LTD in the d eveloping visual cortex.